1. Technical Field
This invention generally relates to an irrigation apparatus for variable water and chemical application, and more particularly to an automatic control system for irrigation machinery for variable water and chemical application in a field, dependent upon varying criteria within the field.
2. Background Art
The use of sprinkler irrigation equipment has, for many years, been one of the most effective and efficient methods of providing irrigation water to growing crops. Technological advances and developments with regard to irrigation equipment have enabled farmers to pump water from whatever source, such as reservoir, irrigation canal, river or water well, through a main irrigation pipeline, to an irrigation system for distribution across the field. Some of the irrigation equipment in common use today can generally be categorized as follows: continuously moving systems, such as center pivot systems, linear line systems, solid set sprinkler line, and wheel lines.
The center pivot system usually embodies a buried main supply line through which irrigation water is pumped, under pressure, to a fixed central pivot tower and up through some sort of a sealed rotatable coupling to a horizontal sprinkler header line which extends radially out from the center pivot assembly. The horizontally oriented sprinkler header line is supported by a plurality of movable support towers, such that the header line can be rotated about the center pivot tower. A plurality of sprinkler assemblies are connected to outlets at spaced intervals along the main line, thus forming a fixed array which is movable. When the main irrigation water supply line and irrigation line are pressurized with a supply of irrigation water, the sprinklers operate automatically to sprinkle the water out over zones of the field located beneath the sprinklers. There are two types of sprinklers in common use today, the first is the impact sprinkler which requires a relatively high pressure supply of water and a spring-loaded rocker baffle, which repeatedly impinges upon the flow of water from the sprinkler nozzle to break it into droplets, with the momentum of the baffle impacts being used to rotate the sprinkler head about a central axis. The second type of sprinkler assembly uses passive baffle plates, wherein a stream of water is discharged through a nozzle and impinges upon a fixed or rotating distribution baffle which disperses the water over the zonal surface area below the pivot irrigation line.
While pivot irrigation systems can be sized to irrigate a circular or arcuate section of a field of virtually any size, typically they are sized to irrigate fields of approximately 160 acres. These are one-half mile in length and are commonly called quarter sections, and utilize ten to fifteen movable towers supporting a main sprinkler header having between 100 and 150 sprinkler assemblies. By its inherent design, the ground speed of the sprinkler header line increases the farther away from the center point, and as a result the nozzles through which the water passes from the main header to the sprinkler assemblies are sized to deliver the least flow rate of water close to the center pivot assembly, and the most water at the farthest point along the main header, so that the radial distribution of water along the line from the center pivot assembly to the outermost nozzle is uniform. For purposes of this disclosure, this shall be referred to as "uniform radial distribution of water". Please see prior art FIG. 4.
The total amount of water, delivered by the distribution system across the field, is determined by the rate of rotation of the pivot towers. Commonly, each of the movable towers is supported by two to four wheels, at least one of which is driven by an electrical or hydraulic motor using some sort of a gear reduction system to synchronize the speeds of the towers, with the outermost towers traveling fastest, and the innermost the slowest. While it is possible to provide variable speed motors to adjust the angular rotation rate of the tower assemblies to either increase or decrease the speed at which the tower assemblies rotate, in practice the preferred commercial method of achieving this goal is to operate or move the tower assemblies intermittently from angular position to position around the field. Typically this is accomplished by use of an electrical control system which turns on and off the electrical motor of the outermost tower to rotate this tower. The electrical motors of the intermediate towers are controlled by a set of electromechanical switches which turn on and off to keep the intermediate towers in alignment with the outermost tower as it travels around the field. Power to each of the tower motors is provided by means of a common line strung parallel to the sprinkler header and energized through a slip ring assembly at the pivot center tower. If the center pivot assembly is to operate at maximum speed, the electrical power system for the outermost tower is on at all times, and to operate at half speed, a 50% cycle would be utilized wherein the electrical motor at the outermost tower is energized 50% of the time, for example, 30 seconds out of every 60 seconds, thus causing the pivot assembly to move at intermittent intervals, resulting in an average rotation of half of full speed.
The second common type of continuously moving self-propelled system is the linear move system, wherein a main irrigation water supply line is positioned along one side of the field, and a sprinkler header, supported at spaced intervals by movable towers and/or wheels extends out normal to the main irrigation line and transverse across the field. As with the center pivot irrigation system, a plurality of sprinkler assemblies are provided at spaced intervals along the sprinkler header. Hydraulic connection between the main irrigation supply system and the sprinkler header is commonly provided by means of a suction pipe in a canal, or a flexible connecting line which connects the inlet of the sprinkler header to any one of a plurality of main line connectors which are spaced at intervals along the main supply line. The transverse sprinkler and sprinkler header assembly, with the sprinklers in a line abreast formation, is then linearly advanced across the field while being supplied with pressurized water. More technologically advanced linear systems utilize two flexible line connectors which are automatically connected to the main line discharge headers one after the other in leap-frog fashion.
The third irrigation system relevant to which the present invention is the stationary irrigation system, which is essentially a lattice grid of fixed irrigation pipe connected to a main irrigation supply line and having a plurality of spaced apart risers and sprinkler heads for distributing water over the field. In these systems, the main irrigation supply line functions as a supply manifold, with each of the fixed sprinkler header lines having a supply valve which opens and closes to supply water to its appendant sprinkler heads.
A fourth type of irrigation system is really a hybrid combination between the linear move system and the stationary, and is called the wheel line irrigation system. Like the linear move system, the wheel line irrigation system utilizes a main irrigation water supply line positioned along one side of the field and a sprinkler header, supported at spaced intervals by wheels which typically use the sprinkler header as a common axle for movement transversely across the field. Unlike the linear move system though, the wheel line is moved, usually by a gasoline engine, from one mainline connector position to the next, and then stopped and held stationary while irrigating a particular transverse zone of the field. In this aspect, the wheel line system is similar to the solid set in that the sprinklers are stationary at the time that water is being distributed across a particular zone of the field.
Each of these systems is designed for, and often times incorporates, features enabling the introduction of chemicals, be they fertilizers, pesticides or other types of agricultural chemicals, into the irrigation water being sprinkled over the field. In practice, it is quite common to introduce nitrates, nitrogen and phosphorous fertilizer, usually in the form of a liquid solution into the irrigation water as the field is being irrigated.
In all four systems, one of the important design parameters is the ability to deliver a uniform supply of water across the entire field. The problem, however, is that it is not necessarily appropriate to uniformly distribute irrigation water, and/or chemicals, across the entire field. Large agricultural fields often times present varying conditions, both as to soil type, texture, topography, drainage, and insect and weed population density. For example, in large fields, one portion of the field may contain thin sandy soil which does not have the capacity to hold large quantities of water or chemicals, and from which water drains easily, and another portion of the field, usually at the bottom of a drainage, which may contain a deeper sand, clay and silt mixture for soil, which drains poorly and holds water and chemicals for a longer period of time. In such cases, if water is distributed by the irrigation system uniformly across the field, the farmer will be faced with the dilemma of having too little water in one portion of the field and too much at the other, if the farmer applies water at a rate equal to the average required over the field. The farmer will not usually do this, since it is an economic necessity that the farmer maximize the economic return from the field. As a result, the farmer will instead often irrigate the entire field at the rate required for the most deficient soil in the field. This is a waste of precious water and the energy needed to pump it. Additionally, this might result in a decreased yield trade off between crop losses caused by under watering a portion of the field as opposed to over watering another portion.
The problems so encountered are further compounded with the use of chemical fertilizers and pesticides, wherein deficient portions of the field soil require extra fertilizer or pesticide. If the farmer markes a uniform application of agricultural chemicals based on the requirements of the deficient soil, it will result in over application in portions of the field. This is a waste of resources and money and often times will result in the leaching of soluble and mobile and chemicals into ground water or waste water recovery systems.
The goal for the farmer in today's competitive market is to apply the correct amount of water and the correct amount of fertilizers, herbicides and other chemicals to the crops as needed, and where needed.